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Discuss how to create ionized gas, accelerate it, guide it and contain it in the context of propulsion.
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Say we have a stream of ionized particles of mixed charge, the positive ions and negative ions can be separated by passing the stream through a magnetic filed perpendicular to the velocity. Once separated, each stream can be individually accelerated.
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If you had an extremely powerful separator maybe, but the plasma is held together pretty tightly by the static attraction between the particles being close together.
Also not sure why this would be any better or easier than an Ion engine or the VASIMR.
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Do any nuclear reactors get hot enough to ionize a gas? If so the ion stream could be created by passing a flow of gas by a nuclear reactor. The pipes would rap around the nuclear reactor like a ball or yarn. The gas would start to warm up at the outside of the yarn like structure and when the gas gets near the core it would ionize. A magnetic bubble would guide the ions to a magnetic nozzle where the positive and negative ions are then separated and accelerated faster.
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If you had an extremely powerful separator maybe, but the plasma is held together pretty tightly by the static attraction between the particles being close together.
Also not sure why this would be any better or easier than an Ion engine or the VASIMR.
I was thinking that maybe some hybrid thermal electric could be used. The gas could initially be accelerated through thermal expansion and then if the gas got hot enough to become a plasma the ions could then be separated and further accelerated.
I was also wondering how fast a gas would half to travel before a perpendicular magnetic field could ionize it. Of course it depends on the field but any numbers would be interesting.
Or lets do it this way. Start with the maximum exhaust velocity of a gas core nuclear reactor (is the gas already plasma?) and then ask how big a perpendicular magnetic field it would take to ionize the gas.
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It’s an interesting problem, because even if the force holding the electron to the atom is greater then the perpendicular force exerted by the magnetic field the electron may still escape by quantum tunneling. The real question is what is the rate of ionization.
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Anyway even with standard electric propulsion one could pu an accelerator track at the end of the standard engine. This accelerator track would improve the efficiency of the ion engine. It may also be able to accelerate the solar wind at the same time. If another source of ions was available besides the standard ion engine then the accelerator could serve a duel purpose.
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Opps, I didn't realize you said the plasma is held tightly together. I was thinking ellectrons to attoms. Would it be held togther any tighter then ellectrons to metal (A.K.A the photo ellectric effect)?
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Solar heating could ionize them. Correct?
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A gas with a low enough ionization energy can be ionized with just an electric current. This is how an arcjet rocket engine works. The best fuels for an arcjet usually fall into two categories: heavy molecular weight gases with low first ionization energies (which take less power to ionize but more power to accelerate the plasma) and light molecular weight gases that dissociate into still lighter molecules (which take more power to ionize but less power to accelerate the plasma). It is not necessary to completely ionize all of the gas to start manipulating it like a plasma, but the more you can ionize the faster the exhaust velocity can be.
A spark plug from a car, run at high enough voltage in a small nozzle, could ionize a gas. However, if you want the best performance, it’s best to shape the nozzle for optimum performance. One of the best nozzle shapes is simply two concentric pipes (one inside the other) with the propellant flowing between them. Each pipe serves as a high voltage electrode, and the current arcing between the electrodes flows through the propellant, ionizing it. The current sets up a magnetic field (perpendicular to both the gas flow and current flow, but concentric with respect to the pipes) that accelerates the plasma out of the nozzle at a rate even faster than its thermal expansion would allow. In addition to creating a suitable magnetic field, it's also important to shape the nozzle to allow maximum charge accumulation where you want it (and prevent it where you don't).
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Mmmm many questions...
Overall, a plasma that is composed of charged atoms/nucleii and free electrons cannot be efficently separated by a magnetic or electrostatic field because of the difficulty in making a charge imbalence in the plasma.
It is also unlikly that a magnetic nozzle or ion accelerator will provide much improvement in the performance of short-burn thermal engines such as Nerva-NTR or GCNR, especially since they do not reach high enough temperatures to efficently ionize their fuel. Solar-thermal systems, which have never been tested and have poor performance beyond Earth, don't provide as much heat to the fuel either.
The VASIMR engine works by heating hydrogen so hot that it will all become a plasma (1,000,000K maybe) with microwaves, which has no net electric charge, and protecting the inside of the engine from contact by confining the plasma with a magnetic field. You cannot use ion acceleration since the plasma has no charge and it is impractical to break down the plasma such that you can.
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I t seems that electrons can be striped off the plasma without two much difficulty by applying a strong electric field as M.C Edwards Suggested. This is described in airforce 2025 under the neutral partial beam section. The Electrons return to the plasma when they pass by the cathode.
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Ultimately charged particles are accelerated by an electric field. This could be done simple by have several plates of different change. However, I think stronger electric fields must be produced by a changing magnetic field. I think a megatron works by using a rotating electric field. However since the magatron accelerates the particles in a circle the loose energy. I think particle accelerators change the magnetic field though a toroid to produce an electric field through the axis of the toroid. I think the last option could produce the greatest electric fields. However, it could only accelerate a pulsed beam of chage particles. This is problematic when combining acceleration with thermal nuclear propulsion.
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Excess electrons can be stripped from a Hydride (H-) without too much trouble, but not so easily from a regular Hydrogen plasma, its a little different.
And using charged plates like in an ion engine just isn't going to be an easy option: the exhaust gas for a simple Nerva-NTR engine is at Three Thousand Degrees Kelvin, and will incinerate a charged plate if its made of metal or graphite... Trying to shield a plate from this fantastic heat with a ceramic will be hard since metals and ceramics expand differently when heated, leading to the ceramic shattering. Active cooling would lower the exhaust velocity too.
For a GCNR engine, this is patently impossible, with exhaust temperatures starting in the 25,000K region and going up from there. If not for the LH2 shield gas, the engine itself would melt almost instantly. You aren't going to put anything IN the exhaust stream.
Any kind of exhaust-charging/accelerating scheme's benefit will probably be negated by the weight of the device and its supporting equipment; the kind of fields you are talking about are gigantic to substantially affect the velocity of tons of hydrogen over the space of minutes, its an entirely different circumstance than grams-of-thrust ion engines.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
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It may be a challenging idea but I think it is worth some analysis. The charged plate idea obviously has some engineering challenges. What about if the exhaust passes through a torrid shaped current loop? The exhaust is going pretty fast so maybe, make a really big toroids spaced really far apart so there is plenty of time to accelerate the exhaust. Or it doesn't even need to be a toroid.
Make the truss have equilateral triangle faces which are perpendicular to the exhaust velocity. Have the exhaust pass through the center of these triangular faces. Make these sections out of iron and rap current loops around them so that a magnetic field could pass around the triangular sections.
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How about passing the H2 gas through the structure to cool it as they do in electrical generators? The gas is then transported to a H2 cooler (Heat exchanger) then back to the generator to be used again and again.
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Hydrogen... electrical generators. Uh, no. I'm pretty sure that they don't pump hydrogen through an electric generator to keep it cool, being that hydrogen is the hardest to contain stuff in the universe and its "kinda flamable." You must be referring to Helium which makes more sense.
Using a shield gas to protect an acceleration mechanism will not do alot of good, since it would separate the accelerator from the exhaust gasses with a material that isn't electricly conductive, so the mechanism won't be able to ionize the gasses efficently and will cut into preexsisting ion acceleration.
It would also be really hard to do, making a thin layer of cold hydrogen between the ultrahot metal-melting exhaust and the accelerator plates/coils... I don't see how it would work, since the shield gas would just boil off and the whole thing would melt anyway.
Edit: Oh yes, and the shield gas probably won't block IR radiation very efficently since its so thin (GCNR engines use a thick layer), so the heat from the exhaust would pass right through the shield gas and melt the whole thing anyway.
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No, the heat would be removed by the H2 gas. I worked in comercial power plants for 20 years for Florida Power and light
both Nuclear and Fossil. Trust me When I tell you they use Hydrogen to cool the generators. I have purged them clean numerous times, and it never blew up and killed me.It is safe if done correctly.
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Hydrogen as coolant... no I don't buy it. More than likly the hydrogen just built up from water electrolosys and had to be removed before becoming explosive. "BZZZT, froooosSSSH"
Thin layer of hydrogen or helium gas isn't enough, you are talking temperatures of over three thousand degrees kelvin. Thats Five Thousand Degrees F. A thin sheet of hydrogen, liquid or gas, isn't going to offer enough protection. The kind of heat put off by a running nuclear reactor at these kinds of power levels (NERVA holds the title for the worlds most powerful reactor today) would boil off the shield gas instantly.
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Hydrogen has the highest specific heat of any known substance.
It is the best coolant in the known universe.
The only problems with it are the handling difficulties. That's why very high temperature applications use molten lithium instead (the second best coolant in the known universe) to avoid those nasty explosion risks.
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It is very high, but thats not important for electrical generators, where the weight of the gas doesn't matter.
The issue is trying to put electrically conductive componets near the exhaust stream of a running nuclear thermal rocket engine as possible. The problem is that you need to be quite close to do much good, and the exhaust is hot enough to destroy the componets rapidly. The thickness of the shield gas layer would have to be very thick to protect it, which means large distances and so it won't work.
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Hmm... Yes, thermal ionization of a plasma by conduction is probably a bad idea. The plasma should be ionized by electric current, microwaves, or something that can act on it directly.
That lowers the nozzle temperature considerably.
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Why not place an opposite charge on the chamber that the ions are in so they never touch the sides? Conductive heat would not be an issue.
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A plasma is very charged for its componets, but it has no net charge, so there would be no force imparted.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
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What if you induced a net charge?
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